This is a review of pharmacotherapy in children and adolescents with mental retardation from the perspective of DSM and ICD disorders. The existing research is reviewed in young people with mental retardation but, when data are lacking, we examined the literature from adults with mental retardation and from typically-developing children. The literature is discussed for each of the following disorders: ADHD, anxiety disorders, bipolar disorder, conduct disorder, depression, enuresis, schizophrenia, self injury, and tics and movement disorders. With the possible exception of ADHD, there is a woeful lack of empirical data on most of these disorders in young people with mental retardation. Clinicians will often be forced to extrapolate from data on adults having mental retardation and from typically-developing children. The best policy is probably to treat such patients cautiously, while gathering data on the effects of such therapy in the hopes of beginning a data base.